Colchicine, both in vivo and in rat liver slices, inhibits secretion of albumin and other plasma proteins. In rat liver slices, inhibiton of secretion occurs at 10 to the minus 6th power M with a maximal effect at 10 to the minus 5th power M, and in vivo inhibition occurrs at 10 to 25 micro mole/100 g body weight. Inhibition of secretion is accompanied by a concomitant retention of the non-secreted proteins within the hepatic cell. In vitro vinblastine also inhibits plasma protein secretion, but lumicolchicine, griseofulvin and cytochalasin B do not. The inhibitory effect in vivo is prompt, within 2 minutes, and lasts for up to 3 hours. Colchicine does not affect protein synthesis initially nor does it affect the intracellular movement of secretory protein from the rough endoplasmic reticulum (ER) to the smooth ER, nor from the smooth ER to the Golgi complex. Colchicine appears to hamper secretion by affecting the discharge of secretory proteins from Golgi-derived secretory vesicles into the Space of Disse. Studies are now being performed at elucidating the mechanism by which colchicine affects this process. BIBLIOGRAPHIC REFERENCES: C.M. Redman, D. Banerjee, K. Howell and G.E. Palade, Annals N.Y. Acad. Sci. 253 780-788 (1975). "The step at which colchicine blocks the secretion of plasma protein by rat liver". C.M. Redman, D. Banerjee, K. Howell and G.E. Palade, J. Cell Biol. 66 42-59 (1975). "Colchicine inhibition of plasma protein release from rat hepatocytes."